The present invention relates to a device for artificially weathering or testing the lightfastness of samples, to a UV radiation device, and to a method for operating such a device.
In devices for artificial weathering, an assessment of the weather-governed ageing behavior of a sample, in particular of a planar material sample, is carried out, wherein the sample is subjected to artificial weathering. Such devices usually comprise for this purpose a weathering chamber, in which mounting means for the mounting of samples to be weathered and a radiation source for applying radiation, in particular UV radiation, to the samples are arranged.
In such devices for artificially weathering or testing the lightfastness of material samples, the intention usually is to estimate the service life of materials which, in the application thereof, are constantly exposed to natural weather conditions and thus deteriorate under climatic influences such as sunlight, heat from the sun, moisture and the like. In order to obtain a good simulation of the natural weather circumstances, it is advantageous if the spectral energy distribution of the light generated in the device corresponds as much as possible to that of the natural solar radiation, for which reason xenon emitters have been used as radiation source hitherto in such devices. In addition, a time-lapse ageing test of the materials is substantially obtained by the samples being irradiated in a manner greatly intensified relative to the natural conditions, whereby the ageing of the samples is accelerated. Consequently, after a comparatively short time it is possible to make a statement about the long-term ageing behavior of a material sample.
The material samples examined in artificial weathering devices for the most part consist of polymeric materials. In the latter, the weather-governed deterioration is substantially brought about by the UV component of the solar radiation. The photochemical primary processes that take place here, that is to say the absorption of photons and the generation of excited states or free radicals, are temperature-independent. By contrast, the subsequent reaction steps with the polymers or additives can be temperature-dependent, with the result that the observed ageing of the materials is likewise temperature-dependent.
In the weathering test devices known hitherto, a xenon lamp is usually used as radiation source. Although, as is known, the solar spectrum can be simulated very well with this lamp, the emitted radiation has a relatively high spectral component in the infrared spectral range, which has to be suppressed by filters in order to prevent the samples from being heated to an excessively great extent. Moreover, a commercially available xenon radiation source has only a service life of approximately 1500 hours.
Furthermore, a metal halide lamp can also be used as radiation source, but this lamp has the disadvantage that it cannot be regulated, or can be regulated only with great difficulty. The same also applies to fluorescent lamps, which have likewise already been used as radiation sources in weathering test devices and are disadvantageously associated with a relatively short service life.
Furthermore, all the radiation sources mentioned have the disadvantage that they are not spectrally variable.
A further disadvantage of the above-mentioned conventional radiation sources of weathering test devices is that the latter are relatively unwieldy in accordance with their construction and their driving and therefore cannot be adapted for example to changed conditions with regard to the sample surfaces of the material samples to be irradiated.